This invention relates generally to wireless communication systems, and more particularly to a method and system for automatic color code assignment to radio channels in a wireless telecommunications network. More specifically, the present invention relates to the optimization of color code assignments to differentiate carrier signals from co-channel interference in the network coverage area.
Wireless communication technology has experienced unprecedented growth, fueled by advances in radio frequency, satellite, and microelectronic technologies and the convenience of access to telephony and portable wireless devices. Several technologies have emerged for providing wireless communications, including analog systems such as Advanced Mobile Phone System (AMPS), and digital systems such as Time Division Multiple Access (TMDA, previously called D-AMPS) and Global System for Mobile Communications (GSM). Such systems typically rely on frequency reuse plans to maximize network capacity and operate in interference-limited radio environments.
Because radio spectrum allocated to a wireless network is a limited resource (both in physical and regulatory sense), schemes to reuse the available radio resources among as many subscribers as possible are often employed. Such schemes seek to maximize spectrum allocation efficiency at a specific Quality of Service (QoS). For example, radio spectrum can be divided into many carrier frequencies spaced apart, with a certain number of carrier frequencies assigned to each base station subsystem (BSS) for serving subscribers entering its coverage area. The frequency allocation to cells in the network usually follows a pre-determined frequency reuse pattern such as 7/21, 4/12, or 3/9, etc. The multiple use of the same frequencies or channels in cells with geographical separation ensures radio spectrum efficiency, but introduces undesirable co-channel interference within wireless networks.
One of co-channel interference impacts on wireless communications is to disable the Mobile Station""s (MS) or Base Station Subsystem""s (BSS) ability to recognize the desirable carrier signal from its co-channel disturbances. This impact directly results in degradation of network service quality, especially during radio network access, call setup, and hand-off, etc. If color codes or Supervisory Audio Tones (SAT) are not properly assigned to radio channels, it may be difficult to distinguish a carrier signal from its co-channel interferences, which can result in calls being dropped, hand-off failure, or cross-talk if an MS/BSS picks up a co-channel and co-SAT signal, during a call access or hand-off.
To overcome this problem, color code assignment methodologies are used in wireless communication networks for assisting an MS or BSS to distinguish a carrier signal from its co-channel interferences. A color code set consists of different integral numbers with each assigned to one of several co-channel cells (or frequencies) that are located geographically closest to each other. Based upon the color code value decoded from all received radio signals, an MS/BSS can uniquely identify the desirable message related to a particular color code assigned to the serving cell or channel.
Currently, color code assignments as practiced in different markets is mostly a manual, individual experience based methodology using cell configuration and frequency assignment as the major information source. However, this current approach is facing an ever-increasing challenge both in efficiency and consistency as advanced frequency planning methods such as Adaptive Channel Allocation (ACA) are deployed to handle network growth. Within the framework of advanced frequency planning, the network is always being tuned to reflect real traffic conditions and, as such, the traditional frequency reuse patterns are no longer fully respected. A color code is required to be assigned to each channel instead of each cell. The automatic assignment of color codes to a radio channel using co-interference prediction and co-channel interference measurements has not, until the present invention, been contemplated.
Thus, a method and system for automatically performing color code assignment based upon measured co-channel interference in the network would provide numerous advantages. The system and method described in the present invention are based on an analog wireless network in which Superisory Audio Tones (SAT) are used as color codes. But the method disclosed in the present invention can be applicable to any wireless network where color codes are assigned to radio channels (or cells) to assist MS/BSS identification of desirable carrier signals.
The present invention achieves technical advantages by automatically assigning a color code (SAT) to radio channels in a wireless network based on measured indicators of interferences. With the present invention, a color code can be initially assigned and then re-assigned to optimize the initial color code assignment utilizing Radio Disturbance Recordings (RDR) with subsequent calculation of Accumulated Averaged Disturbances (AAD).
Accordingly, disclosed in one embodiment is a method of automatically adaptively assigning color codes to radio channels in a wireless network comprising the step of assigning an initial color code to a radio channel in the network by predicting interference propagation between co-channel cells in the network. The method also includes the step of automatically optimizing the initial color code assignment when an alternate color code is available that would improve the ability to distinguish co-channels in the network. The optimizing step is performed utilizing Radio Disturbance Recordings (RDR) which are used to provide an interference level value and an associated interference duration value for each color code.
Also disclosed is a system for automatic adaptive color coding in a wireless network having a plurality of cell sites. The system comprises a means for assigning an initial color code to a channel in the network by predicting interference propagation between co-channel cells in the network. The system further comprises a means for automatically optimizing the initial color code assignment of the channel when an alternate color code would improve the ability to distinguish co-channels in the network. RDR measurements are used as indications of each channel""s interference level value and an associated interference duration value for each color code.
A technical advantage of the method and system of the present invention is the use of current color code assignment schemes in which color codes with the least co-channel interference are assigned to radio channels in the network, thus improving network performance during call setup, hand-off and other network functions.
Another technical advantage is the use of existing RDR data to optimize the initial color code assignment, thus eliminating the need for additional measurements or data collection in the network.
Another technical advantage is the use of automation in color code assignment, thus eliminating extensive labor and time involved in manually assigning color codes for the network.